US customers can claim MP3 copies of all past purchases covered by the initiative dating back as far as 1998.

"What would you say if you bought music CDs from a company 15 years ago, and then 15 years later that company licensed the rights from the record companies to give you the MP3 versions of those CDs... and then to top it off, did that for you automatically and for free?" said Amazon CEO Jeff Bezos.

"Well, starting today, it's available to all of our customers - past, present and future - at no cost."